Molecular cloning and expression of the rat angiotensinogen gene

Abstract

To identify tissue- and hormonal-specific DNA controlcis-elements in the rat gene, we have constructed fusion genes consisting of various lengths of the 5′-flanking region of the rat angiotensinogen gene linked to a human growth hormone (hGH) reporter gene and have introduced them into a subclone of rat pancreatic islet tumor cell line (1056A) which expresses the highest level of angiotensinogen mRNA. As a negative control, we have also introduced them into a human choriocarcinoma cell line (JEG-3), which does not express the endogenous angiotensinogen gene. The level of the expression of these fusion genes in these cells was determined by the level of immunoreactive hGH secreted into the culture medium. The expression of angiotensinogen-growth hormone (ANG-GH) fusion genes, pOGH (ANG N-1498/+18), pOGH (ANG N-688/+18), pOGH (ANG N-110/+18), pOGH (ANG N-53/+18), and pOGH (ANG N-35/+18) was 1.0, 1.8, 1.5, 12.0 and 3.0-fold higher, respectively, than the promoterless growth hormone expression vector (pOGH). The addition of dexamethasone (10⁻⁶ M), aldosterone (10⁻⁵ M), and thyroid hormone, L-T₃ (10⁻⁷ M), stimulated the expression of pOGH (ANG N-1498/+18) by 4.0-, 2.5-, and 2.0-fold above the control level, respectively. Combination of dexamethasone (10⁻⁶ M), L-T₃ (10⁻⁷ M), and ethinyl-estradiol (10⁻⁶ M) stimulated the expression of the pOGH (ANG N-1498/+18) to greater than 10-fold over the control. Ethinyl-estradiol (10⁻⁶ M) or progesterone (10⁻⁶ M) alone had no effect on the expression of the pOGH (ANG N-1498/+18). These studies demonstrate that the induction of expression of the angiotensinogen gene by dexamethasone and L-T₃ in 1056A cells is due to a transcriptional mechanism and the 1056A cells could be useful for studying angiotensinogen gene regulation and for identifying the glucocorticoid and L-T₃-responsivecis-regulatory elements in the angiotensinogen gene.